Shaft for anchoring a hip joint prosthesis in the femur

ABSTRACT

A profiled shaft for anchoring a hip-joint prosthesis in the femur is disclosed, with a shaft section and a fixation section that is formed at the end of the shaft section and that serves for the fixation of a spherical joint head, wherein the shaft section on the lateral surface in the proximal region merges with a trochanter wing at the edges of which beveled surfaces are formed. The essential point of the invention is that the angle formed between the plane of a beveled surface and the plane of the adjacent lateral surface is smaller than 135° and larger than 90°. In a construction of this kind the advantage of an improved filling of the empty space in the trochanter-wing region is achieved.

The invention relates to a profiled shaft for anchoring a hip-jointprosthesis in the femur, with a shaft section and a fixation section,formed at the end of the shaft section, which serves for the fixation ofa spherical joint head, wherein the medial narrow side of the shaftsection merges with a continuously curved arch that ends in the regionof the fixation section, and wherein the lateral side of the shaftsection in its proximal region merges with a trochanter wing on whichthe corners are beveled to form slanted surfaces (facets).

A profiled shaft of this kind for anchoring a hip-joint prosthesis inthe femur is known, for example, from U.S. Pat. No. 5,456,717.

The purpose of the beveled surfaces (facets) is to achieve a better fitof the trochanter-wing region of the profile shaft when it is seated inthe femoral opening.

The conventional practice is to use a facet angle of 45° or 135° (anglebetween the plane of the lateral side and the plane of the adjacentfacet of interest).

However, this specification of the facet angle has proved to producecomparatively large empty spaces in the corner regions of the trochanterwing.

The object of the present invention is to create a profiled shaft of theabove-mentioned kind, for the anchoring section of a hip-jointprosthesis in the femur, such that the empty space in thetrochanter-wing region can be substantially reduced by particularlysimple measures.

This object is achieved in accordance with the invention by developingthe profiled shaft of the kind cited above in such a way that the anglebetween the plane of a beveled surface (facet) and the plane of theadjacent lateral side surface is made smaller than 135° and larger than90°.

An especially advantageous and effective embodiment of the inventionfurther consists in restricting the above-mentioned angle to the rangebetween 100° and 120°.

Furthermore, an especially improved filling of the empty space in thetrochanter-wing region can be achieved by forming a beveled surface(facet) at the transition between the lateral surface of the shaft andthe anterior (broad) surface, and between the lateral surface of theshaft and the posterior (broad) surface of the shaft.

The invention is further characterized in that the beveled surfaces areconstructed as facets with unequal angles at their two ends.

An especially advantageous embodiment of the invention, in the case of aprofiled shaft in which the shaft section on its lateral aspect mergeswith the trochanter wing in the form of a continuously bending curve,consists in a change in the configuration of each of the beveledsurfaces in the region of the continuously bending curve, such that inthe direction from the shaft region to the trochanter region anequal-angled facet changes to one with unequal angles.

In this case the change from equal-angled facet to unequal-angled facetcan take the form of a gradual transition or, in an alternativeembodiment, there can be a stepwise change from equal-angled facet tounequal-angled facet.

In the following the invention is explained in detail with reference toexemplary embodiments and the drawings, wherein

FIG. 1 is a perspective view of a profiled shaft for anchoring ahip-joint prosthesis in the femur with characteristics according to theinvention;

FIG. 2 is a sectional, partially exploded drawing of a profiled shaft inthe implanted state with characteristics according to the invention;

FIG. 3 is an enlarged view of a corner region of the trochanter wing inthe implanted state;

FIG. 4 is a partial anterior view of the upper section of the profiledshaft with characteristics according to the invention;

FIG. 5 is an enlarged view of a corner region of the shaft at a distalportion;

FIG. 6 is a cross section of a profiled shaft with unequal anglesbetween a beveled surface and a plane of an adjacent lateral surface;and

FIG. 7 is a cross section of a profiled shaft with equal angles betweena beveled surface and a plane of an adjacent lateral surface.

FIG. 1 gives a perspective view of an exemplary embodiment of a profiledshaft in which the characteristics according to the present inventionare implemented. The profiled shaft shown here is in general designatedby 1 and comprises a lower, distal, narrow end 5 and a section 7 thatexpands upward and in its upper end region is continuous with a section3 in the shape of a truncated cone that serves for the fixation of aspherical joint head. On the medial narrow side 12 in the proximalregion the shaft has the form of a continuously bending curve 8, whichultimately ends in the region of the fixation section 2.

On the lateral side (anterior broad side 16) the shaft section merges inits proximal region with a trochanter wing 4, on which beveled cornersurfaces 6 (facets) are formed. The anterior broad side 16 issubstantially parallel to a posterior broad side 20 (FIG. 2).

In the conventional construction the angle between the plane of eachbeveled surface 6 and that of the adjacent lateral surface 9 is 135° (or45°).

As can be seen in FIG. 2, which shows a partial view of a section alongthe line A—A in FIG. 1 (in implanted state), the beveled surfaces 6 aand 6 b are oriented with respect to the plane of the lateral surface 9at a steeper angle in comparison with the state of the art; that is, theangle α formed between the plane of a beveled surface 6 a or 6 b and theplane of the lateral surface 9 adjacent to the respective beveledsurface is smaller than 135° and larger than 90°.

In a particularly preferred embodiment of the invention the angle α iswithin the range between 100° and 120°.

In FIG. 3 the left corner region is shown, again in section, as anenlarged partial view in which the embodiment according to the state ofthe art is indicated by a dashed line. It is evident in FIG. 3 that inthe construction in accordance with the invention the empty spacebetween the trochanter-wing region and the surrounding bone is very muchsmaller than, for comparison, in the conventional construction; that is,the construction in accordance with the invention achieves a betterfilling of the empty space in the trochanter-wing region.

It should be noted that in the construction in accordance with theinvention a beveled surface (facet) is formed at the transition betweenthe lateral surface of the shaft and trochanter wing and the anteriorsurface as well as at the transition between the lateral surface of theshaft and trochanter wing and the posterior surface of the shaft.

The beveled surfaces in the construction in accordance with theinvention are in particular formed as facets with unequal angles attheir two ends.

Another embodiment of the present invention is shown schematically inFIG. 4. Here the upper section of the profile shaft, with the trochanterwing 4′, is shown enlarged. In the embodiment shown in FIG. 4 thetransition between lateral surface of the shaft section in its proximalregion and the trochanter wing 4′ has the form of a continuously bendingcurve 10.

The essential feature of this embodiment is that within the region ofthe continuously bending curve 10, at about the level of reference lineB, each of the beveled corner surfaces varies in its orientation alongthe direction from the shaft region to the trochanter region, changingfrom an equal-angled facet as shown in FIGS. 5 and 7 to a facet withunequal angles as shown in FIG. 6.

This embodiment offers the special advantage that the facet with unequalangles is mechanically simpler to produce, for example by rotating theshaft about its long axis during manufacture or by a correspondingrotation of the machining tool.

In an advantageous configuration of the embodiment shown in FIG. 4 thechange from equal-angled facet to facet with unequal angles takes theform of a smooth transition.

Another embodiment consists in changing from equal-angled facet to facetwith unequal angles in a stepwise manner.

It should be pointed out that the present invention is not limited tothe exemplary embodiments shown here, and that a number of modificationsand changes can be undertaken without exceeding the scope of the presentinvention.

For example, it would be possible to construct not only one transitionalregion from equal-angled facet to facet with unequal angles, asdescribed above, but rather to incorporate several transitions of thiskind within the region of continuous curvature.

LIST OF REFERENCE NUMERALS  1= Profiled shaft  2= Fixation section  3=Section in form of truncated cone  4= Trochanter-wing region  5= Distalend  6= Beveled edge surface  6a, 6b= Beveled edge surface  7= Expandingsection  8= Continuously curving arch  9= Lateral surface 10=Continuously curving arch A—A= Line 4′= Trochanter wing α= Angle

What is claimed is:
 1. A profiled shaft for anchoring a hip-jointprosthesis in a femur, comprising: a shaft section having a generallyrectangular cross section and having a proximal region, a distal region,a lateral side and a medial narrow side, wherein a trochanter wing iscontinuous with the lateral side of the shaft section in the proximalregion, wherein the trochanter wing has an anterior broad side and aposterior broad side that are substantially perpendicular to the lateralside, wherein the trochanter wing has beveled edge surfaces, and whereinan angle formed between a plane of a beveled surface and a plane of anadjacent lateral surface is smaller than 135° and larger than 120°,wherein the shaft section on the lateral side merges with the trochanterwing in the form of a continuously bending curve, wherein each bevelededge surface has a first end at the lateral surface and a second end atthe broad side, wherein the angle at the first end is different fromanother angle at the second end within the shaft section, wherein theangle at the first end is equal to the another angle at the second endat the trochanter wing, and wherein each beveled edge surface changesfrom an equal-angled facet to a facet with unequal angles within theregion of the continuous curvature and in a direction from the shaftsection to the trochanter region; and a fixation section formed at anend of the shaft section, which serves for a fixation of a sphericaljoint head, wherein the medial narrow side of the shaft section in theproximal region merges with a continuously curved arch that ends in aregion of the fixation section.
 2. The profiled shaft according to claim1, wherein the change from equal-angled facet to facet with unequalangles takes the form of a smooth transition.